Also, proms involve very young people, let me tell you what I told my sons and nephews, if these girls accept, then hedge their bets, chances are they think an upgrade is out there some where. Don't ever let people (dates) make you feel like the loser. This advise might come too late but if there is still time, tell her you want her to have a great time with someone else. Young men can go stag, girls seldom do. Look around, sometimes shy girls really bloom when invited to the prom.
Take a chance, the worst thing that can happen is you decide not to go. I skipped my junior prom, but I did have a boyfriend who asked me to our senior prom. He dumped me, but said he would ask one of his friends to take me. At the age of 18 I told him that my mother had spent a ton of money on all the accoutrements necessary to look ready for a prom, and I refused to let him off the hook. He agreed to take me. We went, we didn't have a great time
together, but at least I didn't go with a stranger. And I didn't have to sit next to the youngster who was supposed to replace me
We never dated again, and that was acceptable, but dumping me 4 days before the prom was not. This happened during the Bronze Age, when seniors didn't rent limos, take a cruise, whatever. If you have time to nip this in the bud, nip it. Don't let anybody make you feel less than you are.